This invention relates to the transmission of real time data between a sender and receiver over a transmission network.
The current delivery of real-time data depends very much on the feed back channel from the receiver to the sender which provides a report on the received data transmission. Based on this feedback report, the sender will take appropriate action for the transmission of subsequent data to the receiver. The action taken by the sender may require reservation of more network resources for end-to-end data delivery and re-transmission of lost data. Re-transmission of lost data requires the receiver end to report specifically the amount of lost data encountered before the entire data can be of use to the applications at the receiver end. For a large system having a large number of servers and clients, the report messages between the terminals utilise a considerable amount of bandwidth.
In both connection and connectionless data networks, data packets at the lower layers such as the network layer differentiate data only by priority or time-to-live parameters. The distinction made between data packets at the network layer does not relate the coupling nature of the application layer data fragmented into data packets for network layer delivery. Some of these data packet parameters used to distinguish the various classes of service between data packets are listed in the IETF (Internet Engineering Task Force) RFC 791 on Internet Protocol version 4 and IETF's RFC 2460 on Internet Protocol version 6. In the current specifications for Differentiated Service as mentioned in IETF's RFC 2474, RFC 2475, RFC 2597 and RFC 2958, only a means to provide data packet marking is provided. IP data packets with special marking allow the network components such as routers or switches to treat the IP data packets based on the packet's different Quality of Service fields or DSCP, as an indicator on how data flow should be determined. The re-transmission and dropping of data packets belonging to a specific stream is performed at the IP packet level without any knowledge of the application data. Data packet differentiation is only performed at the packet level and selective dropping of a group of data packets is almost impossible if this process has to be performed at the network level.
Without the additional information from the application software, a data packet that makes it though the network may consist of only part of the data the application software needs. With the re-transmission of the missing data that finally arrives at the receiver end, a strict real-time requirement in most instances cannot be met. A data object that arrives not adhering to the real-time requirement is said to be of no presentation value because the time for decoding the piece of information has already passed. As a result, network resources are used in delivering real-time data of no value to the end user. In addition, the non-presentation value group of data packets may cause unnecessary network congestion at the already strained intermediate network nodes. In many instances the congestion of network traffic may be prolonged and in a worst case scenario the traffic congestion may spread to a wider area.
For most real-time data streaming across a packet data network, the decoding rate for the data is only made known to the end devices, for instance the server and the end client. In many instances, the server can only deliver data at the rate based on the decoding rate of the data and a report sent from the client giving statistics of the data received. In some implementations, a large data buffer or an arbitrary size of data buffer needs to be pre-allocated at the client side before the streaming of data from the server to the client can begin. In the scenario where a wide area network is constructed based on a number of intermediate network nodes such as routers and switches which have no information on the type of data and how the data should be treated for end-to-end delivery, the intermediate nodes have no real-time streaming knowledge of the network packets arriving and leaving the nodes. In the event of network congestion at one of the intermediate nodes there is no means to deliver or re-schedule the delivery of network data packets that makes sense from the view of the application data. In most cases only a partial object data is successfully delivered to the end terminals and re-transmission of lost data may be performed automatically by the network layer.